Experts and BHG readers answer.
Lacy leaves on tomatoe plants
I'm sorry --- but without being able to examine your plant, I can't say what's eating it. Have you examined it closely for pests? One of the most common culprits is tomato hornworms [http://www.bhg.com/gardening/pests/insects-diseases-weeds/hornworms/ ] -- but there are others to watch for.
---Justin, Senior Garden Editor, BHG.com